Not Applicable
1. Field of the Invention
The present invention relates generally to the modification and control of the temperature of a selected body organ. More particularly, the invention relates to applications of selective organ cooling which advantageously employ complementary techniques.
2. Background Information
Organs in the human body, such as the brain, kidney and heart, are maintained at a constant temperature of approximately 37xc2x0 C. Hypothermia can be clinically defined as a core body temperature of 35xc2x0 C. or less. Hypothermia is sometimes characterized further according to its severity. A body core temperature in the range of 33xc2x0 C. to 35xc2x0 C. is described as mild hypothermia. A body temperature of 28xc2x0 C. to 32xc2x0 C. is described as moderate hypothermia. A body core temperature in the range of 24xc2x0 C. to 28xc2x0 C. is described as severe hypothermia.
Hypothermia is uniquely effective in reducing brain injury caused by a variety of neurological insults and may eventually play an important role in emergency brain resuscitation. Experimental evidence has demonstrated that cerebral cooling improves outcome after global ischemia, focal ischemia, or traumatic brain injury. For this reason, hypothermia may be induced in order to reduce the effect of certain bodily injuries to the brain as well as other organs.
Cerebral hypothermia has traditionally been accomplished through whole body cooling to create a condition of total body hypothermia in the range of 20xc2x0 C. to 30xc2x0 C. However, the use of total body hypothermia risks certain deleterious systematic vascular effects. For example, total body hypothermia may cause severe derangement of the cardiovascular system, including low cardiac output, elevated systematic resistance, and ventricular fibrillation. Other side effects include renal failure, disseminated intravascular coagulation, and electrolyte disturbances. In addition to the undesirable side effects, total body hypothermia is difficult to administer.
Catheters have been developed which are inserted into the bloodstream of the patient in order to induce total body hypothermia. For example, U.S. Pat. No. 3,425,419 to Dato describes a method and apparatus of lowering and raising the temperature of the human body. Dato induces moderate hypothermia in a patient using a metallic catheter. The metallic catheter has an inner passageway through which a fluid, such as water, can be circulated. The catheter is inserted through the femoral vein and then through the inferior vena cava as far as the right atrium and the superior vena cava. The Dato catheter has an elongated cylindrical shape and is constructed from stainless steel. By way of example, Dato suggests the use of a catheter approximately 70 cm in length and approximately 6 mm in diameter. However, use of the Dato device implicates the negative effects of total body hypothermia described above.
Due to the problems associated with total body hypothermia, attempts have been made to provide more selective cooling. For example, cooling helmets or headgear have been used in an attempt to cool only the head rather than the patient""s entire body. However, such methods rely on conductive heat transfer through the skull and into the brain. One drawback of using conductive heat transfer is that the process of reducing the temperature of the brain is prolonged. Also, it is difficult to precisely control the temperature of the brain when using conduction due to the temperature gradient that must be established externally in order to sufficiently lower the internal temperature. In addition, when using conduction to cool the brain, the face of the patient is also subjected to severe hypothermia, increasing discomfort and the likelihood of negative side effects. It is known that profound cooling of the face can cause similar cardiovascular side effects as total body cooling. From a practical standpoint, such devices are cumbersome and may make continued treatment of the patient difficult or impossible.
Selected organ hypothermia has been accomplished using extracorporeal perfusion, as detailed by Arthur E. Schwartz, M.D. et al., in Isolated Cerebral Hypothermia by Single Carotid Artery Perfusion of Extracorporeally Cooled Blood in Baboons, which appeared in Vol. 39, No. 3, NEUROSURGERY 577 (September, 1996). In this study, blood was continually withdrawn from baboons through the femoral artery. The blood was cooled by a water bath and then infused through a common carotid artery with its external branches occluded. Using this method, normal heart rhythm, systemic arterial blood pressure and arterial blood gas values were maintained during the hypothermia. This study showed that the brain could be selectively cooled to temperatures of 20xc2x0 C. without reducing the temperature of the entire body. However, external circulation of blood is not a practical approach for treating humans because the risk of infection, need for anticoagulation, and risk of bleeding is too great. Further, this method requires cannulation of two vessels making it more cumbersome to perform particularly in emergency settings. Even more, percutaneous cannulation of the carotid artery is difficult and potentially fatal due to the associated arterial wall trauma. Finally, this method would be ineffective to cool other organs, such as the kidneys, because the feeding arteries cannot be directly cannulated percutaneously.
Selective organ hypothermia has also been attempted by perfusion of a cold solution such as saline or perflourocarbons. This process is commonly used to protect the heart during heart surgery and is referred to as cardioplegia. Perfusion of a cold solution has a number of drawbacks, including a limited time of administration due to excessive volume accumulation, cost, and inconvenience of maintaining the perfusate and lack of effectiveness due to the temperature dilution from the blood. Temperature dilution by the blood is a particular problem in high blood flow organs such as the brain.
The invention provides a practical method and apparatus which modifies and controls the temperature of a selected organ and which may be used in combination with many complementary therapeutic techniques.
In one aspect, the invention is directed towards a device for heating or cooling a surrounding fluid in a feeding vessel. The device includes a catheter assembly capable of insertion to a selected feeding vessel in the vascular system of a patient. The assembly includes a heat transfer element at a distal end of the catheter assembly, the heat transfer element having a plurality of exterior surface irregularities shaped and arranged to create turbulence in a surrounding fluid, the surface irregularities having a depth at least equal to the boundary layer thickness of flow of the surrounding fluid in the feeding vessel. The surrounding fluid may be, e.g., blood in a blood vessel, working fluid within the heat transfer element, etc., and combinations thereof. The assembly further includes a supply catheter to deliver a working fluid to an interior of the heat transfer element and a return catheter to return a working fluid from the interior of the heat transfer element. A drug delivery catheter is also provided and runs substantially parallel to the axis of the catheter assembly.
Implementations of the invention may include one or more of the following. The drug delivery catheter may be disposed substantially coaxially with respect to the supply catheter. The drug delivery catheter may include an outlet at a distal end thereof, the distal end of the drug delivery catheter distal of a distal end of the return or supply catheters. The drug delivery catheter may be disposed within one of the return catheter or the supply catheter or both, and may include an outlet transverse or parallel to the axis of the catheter assembly. The surface irregularities may include a helical ridge and a helical groove formed on each of successive heat transfer segments; and the helical ridge on each heat transfer segment may have an opposite helical twist to the helical ridges on adjacent heat transfer segments. At least one sealed lumen within one of the return catheter or the supply catheter or both may be provided, the sealed lumen in pressure communication with a supply of air to inflate the sealed lumen. The return catheter may be coaxial with the supply catheter, and the return catheter have a larger or smaller radius than the supply catheter, depending on the requirements of the user.
In another aspect, the invention is directed to a device for heating or cooling a surrounding fluid in a feeding vessel. In this aspect, the heat transfer element has a distal end which defines an orifice. A supply catheter deliver a working fluid to an interior of the heat transfer element, the supply catheter having a working fluid catheter disposed therein and further having disposed therein a drug delivery catheter running substantially parallel to the axis of the supply catheter. The working fluid catheter has defined thereon a number of outlets to communicate the working fluid from the interior of the supply catheter to a volume defined by the exterior of the supply catheter and the interior of the heat transfer element. The device further includes a return catheter to return the working fluid from the interior of the heat transfer element.
In yet another aspect, the invention is directed to a method for selectively controlling the temperature of a selected volume of blood in a patient. The method includes introducing a catheter assembly into a blood vessel feeding a selected volume of blood in a patient, and delivering a working fluid through a supply catheter in the catheter assembly and returning the working fluid through a return catheter in the catheter assembly. Heat is transferred between a heat transfer element forming a distal end of the catheter assembly and the volume of blood in the feeding vessel. A liquid is delivered through a drug delivery catheter to the volume of blood in the feeding vessel.
Implementations of the invention may include one or more of the following. Turbulence may be created around a plurality of surface irregularities on the heat transfer element at a distance from the heat transfer element greater than the boundary layer thickness of flow in the feeding vessel, thereby creating turbulence throughout a free stream of blood flow in the feeding vessel. The surface irregularities on the heat transfer element may include a plurality of segments of helical ridges and grooves having alternating directions of helical rotation; and turbulence is created by establishing repetitively alternating directions of helical blood flow with the alternating helical rotations of the ridges and grooves. The liquid may be a warm enzyme solution, and may be selected from the group consisting of tPA, streptokinase, urokinase, pro-urokinase, and combinations thereof. The liquid may be delivered to the volume in a longitudinal or transverse direction with respect to the axis of the catheter assembly. The liquid may be delivered to the volume proximal or distal of the distal tip of the catheter assembly. If the volume of blood includes a blood clot, during the delivering of the liquid the distal tip of the catheter assembly may be disposed substantially near, adjacent, or embedded in the blood clot. Air may be delivered to at least one sealed lumen within the return catheter to cause the sealed lumen to enlarge. The air may further be delivered in a pulsatile fashion to repeatedly enlarge and contract the sealed lumen, thereby to create additional turbulence, e.g., to enhance heat transfer.
Advantages of the invention include the following. The device may be placed in an artery without traumatizing the arterial wall and with damaging the device itself. The device may be placed in an artery simply and by a variety of practitioners such as cardiologists or neurosurgeons. The device allows the complementary performance of simultaneous procedures along with brain cooling, these procedures including angiography, stenotic lesion stenting, and drug delivery.
The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which: